1. Field of the Invention
The present invention relates to a turbocharger.
2. Related Background Art
A conventional turbocharger is one disclosed in Japanese Patent Application Laid-open No. 9-242554 (U.S. Pat. No. 5,993,173 corresponding thereto). This turbocharger is provided with a housing having a bearing housing in which a bearing chamber is formed, a semi-floating bearing arranged in the bearing chamber, and a rotor shaft rotatably supported by the semi-floating bearing. A turbine wheel and a compressor wheel are coupled to the two ends of the rotor shaft.
The semi-floating bearing has a pair of bearing portions formed at the two longitudinal ends, and an intermediate portion connecting the two bearing portions. Formed in each of the two bearing portions are a first outer peripheral surface of a cylindrical shape, and a first inner peripheral surface arranged coaxially with the first outer peripheral surface and rotatably supporting the rotor shaft.
Formed in the bearing housing are an outside oil feed chamber located between the bearing housing and the intermediate portion, a first oil feed passage which can supply a lubricant oil to the outside oil feed chamber, and a second inner peripheral surface supporting each of the first outer peripheral surfaces. Formed in the intermediate portion are an inside oil feed chamber located between the intermediate portion and the rotor shaft, and a second oil feed passage making the outside oil feed chamber communicated with the inside oil feed chamber.
In the bearing chamber, oil drain grooves extending downward are formed in the turbine-wheel-side end face and in the compressor-wheel-side end face, respectively. The upper end of the oil drain groove on the turbine wheel side is opposed to a thrust receiving member arranged to rotate together with the rotor shaft. The upper end of the oil drain groove on the compressor wheel side is opposed to a diameter-increased portion of the rotor shaft.
In this turbocharger, the lubricant oil is supplied through the first oil feed passage and the outside oil feed chamber to the first outer peripheral surfaces of the two bearing portions of the semi-floating bearing and also supplied through the second oil feed passage and the inside oil feed chamber to the first inner peripheral surfaces of the two bearing portions. This configuration allows the semi-floating bearing to rotatably support the rotor shaft well. The lubricant oil supplied to the first outer peripheral surfaces is subjected to supply pressure from the first oil feed passage side, to move toward the turbine wheel and toward the compressor wheel. The moving lubricant oil is guided downward by the oil drain grooves. This improves oil drain performance of this turbocharger.